Radiologic studies play an integral role in detecting, staging, and following patients with cancer. While conventional imaging modalities provide a tremendous amount of anatomic and morphologic information, many lesions remain indeterminate, and invasive procedures are required to establish a diagnosis. The primary goal of this investigation is to develop a novel high-throughput screening platform that exploits a H/D exchange- and mass spectrometry-based technique, termed SUPREX, for the discovery of small molecule protein-ligands that can be used as tumor specific molecular imaging probes. Such molecules would have tremendous clinical utility in non-invasive tests to evaluate anatomic abnormalities that are indeterminate by conventional imaging studies, and to more accurately characterize lesions for targeted therapy. The specific aims of this work are to optimize the throughput and overall efficiency of the new platform and to utilize it in a proof-of-principle study for the lead discovery of potential molecular imaging agents for lung cancer. In the proposed work we will: (1) demonstrate the platform's ability to screen small molecule combinatorial libraries for protein binding at a rate of 6 ligands/min;(2) demonstrate the platform's ability to have a high positive yield (i.e. false positive and false negative rates of less than 10%);(3) screen three small-molecule combinatorial libraries for binding to cyclophilin A (CypA), a protein that is over-expressed in non-small cell lung cancers;and (4) characterize the binding properties of the tightest binding "lead" molecules identified in (3) including: i) their binding affinity, ii) their binding site relative to known ligands, and iii) their ability to specifically detect the overexpression of CypA in whole cel uptake assays.